1. Field of the Invention
The present invention relates to a magnetic storage apparatus and a magnetic storage medium, particularly to a magnetic storage apparatus having a recording density of 50 Gb/in2 or higher and a magnetic storage medium to achieve the recording density.
2.Description of the Related Prior Art
In recent years, an amount of information handled by computers has been steadily increased, and a larger capacity and higher transfer rate are more and more required of a magnetic disk storage device of an external storage device. So far, a magnetic disk storage device having the maximum recording density of 10 Gb/in2 class has been commercialized. This kind of magnetic disk storage device adopts a longitudinal magnetic recording method. However, influence of a so called thermal fluctuation has become conspicuous, in a state where a magnetic energy possessed by becoming extremely fine recording bits decreases as the recording density increases and a recorded magnetization is reversed due to demagnetizing field working at a bit-transition and ambient heat. Therefore, it is considered to be difficult to attain an areal recording density exceeding 40 Gb/in2 in the conventional longitudinal magnetic recording method that uses a recording layer of a Co alloy series.
On the other hand, a perpendicular magnetic recording method is a magnetic recording method, in which magnetization is formed in a direction perpendicular to the surface of a recording medium film and such that adjacent recording bits become antiparallel to each other. Unlike the longitudinal magnetic recording method, the perpendicular magnetic recording method has a small demagnetizing field at the bit-transition, and has a characteristic that the magnetization is stably maintained as the recording density becomes higher. Accordingly, the perpendicular magnetic recording method is considered as one of the strong means for attaining a high recording density that exceeds the thermal fluctuation limit of the current longitudinal magnetic recording method. Media used in the perpendicular magnetic recording method are classified into two types; one is a single layer perpendicular magnetic recording medium having a perpendicular magnetic recording layer formed on a substrate via a non-magnetic underlayer, and the other is a double layer perpendicular magnetic recording medium where a soft magnetic underlayer is formed on a substrate and the perpendicular magnetic recording layer is formed on the soft magnetic underlayer directly or via a non-magnetic intermediate layer. In the single layer perpendicular magnetic recording medium, a ring-type head similar to the one used in the current longitudinal magnetic recording medium is generally used. However, since a gradient of a magnetizing field of the perpendicular magnetic recording is not steep, there is a problem that resolution is not improved. On the other hand, in the double layer perpendicular magnetic recording medium, a single pole type head can be utilized, where a strong magnetizing field of the perpendicular magnetic recording and a steep gradient of magnetizing field are obtained. As a result, it is advantageous that the resolution is improved in comparison with the single layer perpendicular magnetic recording medium. For this reason, a combination of the double layer perpendicular magnetic recording medium and the single pole type head is considered to be effective for commercializing the perpendicular magnetic recording method.
The double layer perpendicular magnetic recording medium can obtain the high resolution, but on the contrary, noise originated in the soft magnetic underlayer is problematic, in addition to noise originated in the recording layer, which can be seen in the single layer perpendicular magnetic recording medium as well. The noise is classified into a spike noise and a transition noise; the former occurs from a magnetic domain wall of the soft magnetic underlayer and the latter occurs by fluctuation of a magnetization transition in the recording layer owing to a magnetization state of the soft magnetic underlayer. With regard to the former spike noise, for example, as disclosed in Japanese Patent Laid-open No. 7(1995)-129946 gazette and Japanese Patent Laid-open No. 11(1999)-191217 gazette, there is a method where a hard-magnetic pinning layer is provided between the soft magnetic underlayer and the substrate to control a magnetic domain structure of the soft magnetic underlayer, thereby the spike noise is reduced. On the other hand, the latter transition noise is observed in a state of superposing the transition noise originated in the recording layer itself. Therefore, details are not yet clear as to how much the magnetization state of the soft magnetic underlayer influences the fluctuation of the magnetization transition in the recording layer.
When it is considered that the perpendicular magnetic recording method in the combination of the double layer perpendicular magnetic recording medium and the single pole type head is applied at the recording density exceeding the thermal fluctuation limit of the longitudinal magnetic recording method, both of a medium noise originated in the recording layer and the medium noise originated in the soft magnetic underlayer need to be reduced. The present invention has been created to solve the above-described problems. More specifically, the object of the present invention is to provide the perpendicular magnetic recording medium having a high medium S/N ratio at the recording density of 50 Gb/in2 or higher, and to facilitate the achievement of a high density magnetic storage device.
Reduction of the medium noise originated in the recording layer is attained, in the perpendicular magnetic recording medium where the soft magnetic underlayer, the intermediate layer and the perpendicular magnetic recording layer are sequentially deposited on the substrate, by forming the intermediate layer with a non-magnetic amorphous alloy, in which Ni is made to be a main component and Zr is contained. Herein, the term xe2x80x9camorphousxe2x80x9d means that a broad peak is observed by a thin-film X-ray diffraction, or that a halo pattern is observed by an electron diffraction.
Heretofore in the single layer perpendicular magnetic recording medium, to improve a perpendicular orientation of the perpendicular magnetic recording layer, there has been considered a method of providing the underlayer of non-magnetic material between the perpendicular magnetic recording layer and the substrate. For example, methods of using the non-magnetic material underlayer are disclosed in: Japanese Patent Laid-open No. Sho 58(1983)-77025 and No. Sho 58(1983)-141435 gazettes in which Ti is used as the underlayer of a Coxe2x80x94Cr perpendicular magnetic recording layer; Japanese Patent Laid-open No. Sho 60(1985)-214417 gazette in which Ge and Si are used as the underlayer; Japanese Patent Laid-open No. Sho 60(1985)-064413 gazette in which an oxide such as CoO and NiO is used as the underlayer; and Japanese Patent Laid-open No. 2000-30236 gazette in which MgO is used.
When the present inventors considered applying such non-magnetic underlayer materials for the intermediate layer of the double layer perpendicular magnetic recording medium, various problems have become clear. In the double layer perpendicular magnetic recording medium, since the intermediate layer is formed on the soft magnetic underlayer, a microstructure of the intermediate layer receives an influence in the case where poly-crystalline materials such as Nixe2x80x94Fe and Fexe2x80x94Alxe2x80x94Si and where amorphous materials such as Coxe2x80x94Nbxe2x80x94Zr and Coxe2x80x94Taxe2x80x94Zr are used for the soft magnetic underlayer. As a result, the c-axis vertical orientation and the magnetic property of the perpendicular magnetic recording layer change significantly. For example, when Ti is used for the intermediate layer, although it shows a relatively good property on the amorphous soft magnetic underlayer, the c-axis vertical orientation of the perpendicular magnetic recording layer is degraded on the poly-crystalline soft magnetic underlayer, there is seen a tendency that a sufficient magnetic property cannot be obtained. In addition, in the double layer perpendicular magnetic recording medium, it is effective that a film thickness of the intermediate layer is made to be thinner in order to increase recording and reproduction efficiency. However, for example, when the amorphous material such as Ge is used for the intermediate layer, it is difficult to make the intermediate layer thin because diffusion easily occurs at the interface.
The present inventors, after considering various materials for the intermediate layer to be formed between the soft magnetic underlayer and the perpendicular magnetic recording layer, found out the following. When the non-magnetic amorphous alloy is used, in which Ni is made to be a main component and Zr is contained, the perpendicular orientation of the perpendicular magnetic recording layer becomes strong and small crystal grains are obtained (regardless of) whether the microstructure of the soft magnetic underlayer is poly-crystalline or amorphous. With a composition of the intermediate layer of an Nixe2x80x94Zr series alloy, the above-described effect is obtained when the layer is non-magnetic and amorphous. By adding at least one kind of element of Nb and Ta, the non-magnetic and amorphous intermediate layer can be formed under various film forming processing conditions. When the intermediate layer of the present invention is used, a change of magnetic property owing to the film thickness of the intermediate layer is small, and deterioration of the magnetic property is not seen even in the case where the film thickness is as thin as 2 nm. In other words, an influence of the structure and magnetization of the soft magnetic underlayer to the perpendicular magnetic recording layer can be efficiently cut off. The reason is considered that the material for the intermediate layer of the present invention has a smaller interfacial diffusion and a higher covering ratio in comparison with the amorphous material such as Ge, Si and C. The film thickness of the intermediate layer is preferably 2 nm or more and 20 nm or less in order to break a magnetic coupling between the soft magnetic underlayer and the perpendicular magnetic recording layer, and to increase the recording-reproduction efficiency. Moreover, the material for the intermediate layer of the present invention can be also used for the underlayer of the single layer perpendicular magnetic recording medium.
Reduction of the medium noise originated in the soft magnetic underlayer is attained, in the perpendicular magnetic recording medium where the soft magnetic underlayer, the intermediate layer and the perpendicular magnetic recording layer are sequentially formed on the substrate, by constituting the soft magnetic underlayer with ferromagnetic nano-crystals precipitated by annealing.
Heretofore, as the material for the soft magnetic underlayer, the poly-crystalline materials such as Nixe2x80x94Fe and Fexe2x80x94Alxe2x80x94Si and the amorphous materials such as Coxe2x80x94Nbxe2x80x94Zr and Coxe2x80x94Taxe2x80x94Zr have been proposed. The present inventors found out that the spike noise seen in the conventional soft magnetic underlayer materials can be reduced and the transition noise originated in the soft magnetic underlayer can be also reduced when a material is used for the soft magnetic underlayer, the material such is substantially amorphous and has a small saturation magnetic flux density at the time of film forming, in which ferromagnetic nano-crystals are precipitated and a high saturation magnetic flux density is obtained by annealing. As a precipitated ferromagnetic nano-crystal, any of xcex1-Fe, fcc-Co and hcp-Co is effective, but xcex1-Fe is the most desirable because a low coercivity and a high saturation magnetic flux density can be easily obtained. For example, when the soft magnetic underlayer is adopted where the xcex1-Fe nano-crystals were precipitated, elements and compositions of the soft magnetic underlayer materials are not specifically limited as long as the materials precipitate the xcex1-Fe nano-crystals. Specific examples of the materials are an Fexe2x80x94Taxe2x80x94C alloy, an Fexe2x80x94Hfxe2x80x94C alloy, an Fexe2x80x94Zrxe2x80x94C alloy, an Fexe2x80x94Nbxe2x80x94C alloy, an Fexe2x80x94Tixe2x80x94C alloy and the like. When any of these materials is used and annealing suitable for each of the materials is performed, xcex1-Fe nano-crystals can be uniformly precipitated. Moreover, the xcex1-Fe nano-crystals can be also obtained by sputtering an Fexe2x80x94Ta alloy or an Fexe2x80x94Hf alloy in an Ar/N2 mixed gas.
Generally speaking, the soft magnetic underlayer can be made to be the one that contains Fe as a first element, at least one of C and N as a second element, and at least one kind of element selected from Ta, Hf, Nb, Ti and Zr as a third element. The soft magnetic underlayer has a small spike noise even if it is directly used. However, when a pinning layer utilizing an interlayer anti-ferromagnetic coupling or a ferromagnetic coupling is provided between the soft magnetic underlayer and the substrate to control the magnetic domains, the spike noise is more effectively reduced.
As the perpendicular magnetic recording layer to be used for the perpendicular magnetic recording medium of the present invention, a Coxe2x80x94Crxe2x80x94Pt alloy, a Coxe2x80x94Crxe2x80x94Ptxe2x80x94Ta alloy, a Coxe2x80x94Crxe2x80x94Ptxe2x80x94B alloy and the like can be used. As a protective layer of a perpendicular magnetic recording layer, a film having a film thickness of 3 nm or more and 10 nm or less with carbon as a main component is formed, in addition, a lubricant layer such as perfluoroalkylpolyether or the like is formed in the film thickness of 1 nm or more and 10 nm or less. Thus, a highly reliable perpendicular magnetic recording medium is obtained.
In the magnetic storage apparatus of the present invention comprising: the above-mentioned perpendicular magnetic recording medium; a driver to drive the medium in a recording direction; a magnetic head consisting of a recording section and a reproduction section; means for allowing the magnetic head to have a relative movement for the perpendicular magnetic recording medium; and recording-reproduction processing means for performing signal input to the magnetic head and reproduction of output signal from the magnetic head, the reproduction section of the magnetic head is constituted of a high-sensitive sensor utilizing any one of a giant magnetoresistive effect and a tunneling magnetoresistive effect. With this constitution, the magnetic storage apparatus having a high reliability at the recording density of 50 Gb/in2 or higher can be achieved.